public class China implements Computable {  //China类实现Computable接口
	   int number;
      	   public int f(int x) { //不要忘记public关键字
	     	   int sum=0;
	    	   for(int i=1;i<=x;i++) {
		 	   sum=sum+i;
	   	   }
	      	   return sum;
	   }
}
